Dutch environment minister Jan Pronk has ordered the closure of the Petten research reactor, following reports of a hairline crack in one of the welds of the reactor vessel.

The European Commission-owned high flux reactor (HFR) was shutdown on 18 February, after a brief delay due to its role in the production of medical radioisotopes for the diagnosis and treatment of cancer patients.

The Dutch energy research organisation, NRG, said: “An audit will be carried out (by the International Atomic Energy Agency) in order to evaluate the safety culture. The period the HFR is not in operation will be used to carry out a number of measurements of one of the welds within the reactor vessel.” A spokeswoman for NRG said a crack had been discovered before the reactor vessel came into operation in 1984. It had been monitored regularly and remained unchanged. Following the introduction of new, more sophisticated monitoring equipment, an additional, smaller crack had been discovered behind the existing one.